Compact and lightweight electrical/electronic devices such as cellular phones, laptops, and computers are actively developed and produced with the development of high technology, and such portable electrical/electronic devices require highly efficient batteries for supplying power thereto. Therefore, it is necessary to develop a highly efficient, ultra-compact, and ultra-light battery. Particularly, all solid-state lithium secondary batteries satisfy such conditions while being able to be charged and discharged in consideration of economic aspects.
The all-solid-state lithium batteries can be manufactured in any size and form, and can maximize electrode/electrolyte interfacial adhesion properties by applying a solid electrolyte with a thickness of a few μm or less on an electrode using a thin film deposition technique. Furthermore, the all-solid-state lithium batteries do not generate heat or gaseous products during operation and thus have a high stability as compared to when a liquid electrolyte is used. The all-solid-state lithium batteries do not cause contamination or leakage problems, have a low electronic conductivity, and thus have an advantage of no self-discharge.
Due to these advantages, it is expected that use of the chargeable/dischargeable all-solid-state lithium secondary batteries will gradually expand. Particularly, with the increase in demands for secondary batteries, which can be used in ultra-compact devices, electrical devices, smart cards, and microelectromechanical systems (MEMS) that require ultra-compact batteries, researches on all-solid-state lithium secondary batteries are rapidly increasing.
Thus, various methods for developing a high capacity all-solid-state lithium secondary battery have been attempted, and particularly, methods for increasing the area or thickness of a cathode have been attempted in order to increase the capacity of the all-solid-state lithium secondary battery. This is because energy density, reversibility, and discharge rate, which are important factors for the efficiency of a general all-solid-state lithium secondary battery, are determined by a cathode material among components of a battery. Therefore, in order to use a battery for a long time with a high energy density, the development of a suitable cathode material is important, and particularly, it is necessary to increase the thickness of a cathode.
Thus, conventionally, as disclosed in KR Patent Publication No. 10-2006-0008049, an electrode for a lithium secondary micro battery and a method for manufacturing the same, the electrode having a thick electrode active material layer formed by applying, on a substrate, a slurry which is formed by mixing electrode active material powder and a sol solution including at least one electrode active material precursor compound respectively including metal elements constituting the electrode active material, are suggested as a technique relating to an electrode for a lithium secondary micro battery providing a high capacity electrode by forming a film thicker than a thin film.
A technique for forming a thick cathode may have an effect of increasing the capacity of a battery due to an increase in the cathode capacity of the battery. However, an increase in the thickness of a cathode results in a decrease in fast charging-discharging efficiency due to the internal resistance, and the like.
Also, when a cathode is manufactured into a thick layer having a thickness of 100 μm or more in order to increase the cathode capacity of a battery, the surface roughness of the cathode increases, thus causing a problem of reducing adhesion properties between the cathode and a solid electrolyte.
Therefore, there is a need for a technique relating to a cathode substrate for an all-solid-state lithium secondary battery, the cathode substrate being capable of increasing the capacity of the battery while having the same thickness as in a conventional substrate, and being capable of decreasing a conduction distance between an electrode and a cathode material.